1. Technical Field
This disclosure relates to an image forming apparatus and a treatment-liquid application device, and more specifically to an image forming apparatus capable of applying treatment liquid to an image recording medium and a treatment-liquid application device to apply treatment liquid to a modification target, for example, an image recording medium.
2. Description of the Background Art
Image forming apparatuses are used as printers, facsimile machines, copiers, plotters, or multi-functional devices having two or more of the foregoing capabilities. As one type of image forming apparatuses, for example, liquid-ejection-type image forming apparatuses are known that use a recording head(s) for ejecting droplets of ink or other liquid. During image formation, such liquid-ejection-type image forming apparatuses eject droplets of ink or other liquid from the recording head onto a recording medium to form a desired image.
Such inkjet-type image forming apparatuses fall into two main types: a serial-type image forming apparatus that forms an image by ejecting droplets from the recording head while moving the recording head in a main scanning direction of the carriage, and a line-head-type image forming apparatus that forms an image by ejecting droplets from a linear-shaped recording head held stationary in the image forming apparatus.
Such a liquid-ejection-type image forming apparatus may have image failures, such as “feathering” in which dots formed with liquid droplets blur in an jaggy shape on the recording medium and “color bleeding” in which different types of liquid droplets (e.g., ink droplets having different colors) mix each other at their adjacent areas. Alternatively, such a liquid-ejection-type image forming apparatus may take a relatively long time to dry liquid droplets on a recording medium after image formation.
To cope with such failures, a treatment liquid may be applied onto the recording medium before image formation to minimize failures, such as feathering or bleeding of droplets landed on the recording medium and reduce the time for drying droplets on the recording medium.
A conventional image forming apparatus includes a treatment-liquid container (treatment-liquid storage unit) to store a treatment liquid and a treatment-liquid application unit to apply the treatment liquid to a recording medium. The treatment liquid stored in the treatment-liquid container is replenish to a chamber of the treatment-liquid application unit through a supply channel. For the image forming apparatus, the chamber is opened to ambient air, and when application of the treatment liquid to the recording medium is not performed, the treatment liquid in the chamber evaporates from the surface of the treatment liquid. As a result, the treatment liquid may be wasted or change its properties due to change in concentration. In particular, when a highly-volatile liquid is used as the treatment liquid, such failures may become prominent.
To cope with such failures, for example, a conventional image forming apparatus retains treatment liquid in a liquid retaining space (chamber) between an application roller and a liquid retaining member and uses the application roller to apply the treatment liquid to the recording medium. The conventional image forming apparatus also includes a supply channel to supply the treatment liquid from a replacement tank (treatment-liquid storage unit) to the liquid retaining space via a buffer tank (temporary storage unit) and a collection channel to collect the treatment liquid from the liquid retaining space to the buffer tank when the application roller is stopped, to prevent or minimize leakage of the treatment liquid from the liquid retaining space. For such a configuration, when the application roller is stopped (application of the treatment liquid is not performed), the liquid level of treatment liquid is positioned within the buffer tank, not the liquid retaining space. The liquid retaining space is directly exposed to ambient air. By contrast, the buffer tank is exposed to ambient air only through the narrow collection channel connected to the liquid retaining space. The channel cross-sectional area of the collection channel is smaller than an area of the liquid level obtained when the liquid retaining space includes the treatment liquid. When the treatment liquid in the liquid retaining space is collected so as to position the liquid level of the treatment liquid within the buffer tank, the evaporation amount of the treatment liquid becomes smaller than in a case in which the treatment liquid is left in the liquid retaining space.
However, for such a configuration, the liquid level of the treatment liquid collected in the buffer tank has an area corresponding to a horizontal cross-sectional area of the buffer tank and contacts ambient air over a relatively large area. Thus, since the treatment liquid evaporates in the buffer tank, the treatment liquid is wasted and change characteristics due to, for example, a change in the concentration.
Alternatively, it is conceivable that a temporary storage unit, such as the buffer tank, is not provided in the collection channel. However, when the treatment liquid is collected from the liquid retaining space, air is also collected along with the treatment liquid. Unless air is removed from the collected treatment liquid, the treatment liquid is resupplied to the liquid retaining space in a foam. As a result, proper resupply of the treatment liquid to the liquid retaining space may be hampered, and the resupply itself may be hampered depending on the structure. Therefore, in a case in which the treatment liquid collected through the collection channel is resupplied, such a temporary storage unit as the buffer tank need be disposed in the collection channel to temporarily store the treatment liquid and separate air from the treatment liquid, thus causing the above-described failures.
In addition, the above-described failures may occur in not only the liquid-ejection-type image forming apparatus but also an apparatus including a treatment-liquid application device to apply a treatment liquid to an application target.